Hearing screening of human infants is not yet wide spread in either the physician's office or the home. Yet it is critical that hearing loss be identified and remedied as early as possible to ensure the highest development of an infant's language skills.
The infant brain is plastic and receptive to language learning mainly in the first two or three years of life. Yet there is a delay of generally two years in the diagnoses of congenitally deaf infants. When hearing losses are more moderate, the delay in diagnosis generally approaches four years.
The primary reason that physicians fail to screen infant hearing is that there has not been available an instrument with a well calibrated acoustic signal that incorporates frequency specific and attractive sounds suitable for identifying hearing loss in the young.
The method and apparatus of this invention provides an answer to this problem in that the invention is not only acceptable to physicians, but also is sufficiently simple to be used by parents.
It would be desirable for parents to be able to test their baby's hearing with a high degree of accuracy. In order to determine if this is a reasonable goal, a project was set up to determine whether parents are able to perform hearing screening, and to develop such an instrument.
In this study, 250 families were given a kit of noisemakers, and an instruction booklet graphically describing use of the noisemakers in screening the hearing ability of their children. Following screening trials, audiologists came to the homes and rated the parents' screening techniques. The audiologists then retested the children, first with the noisemakers, and then with a portable visual reinforcement (PVR) audiometer. Ambient noise measurements were also taken in the homes.
Eighty-eight percent of the parents demonstrated an acceptable screening technique, but only 5% used the noisemakers at an optimally soft level. Ambient noise levels of 60-75 dB during testing were considered responsible for unacceptable loud presentations by the parents.
This test however, produced no statistically significant differences between the parent's testing and the audiologist's testing. From this it can be concluded that parents are in fact able to screen their baby's hearing as well as audiologists can, but parents need a well controlled electronic instrument in order to screen accurately.
The present invention provides such an instrument.
Hearing screening procedures described in the art generally consist of two techniques: (1) With the baby seated on its mother's lap, a second testing individual kneels in front of the baby and extends an arm and a noisemaker low and to one side of the baby as the noisemaker is activated. The expected response from the baby is a turn of the head to the side where the noisemaker is located, and (2) One person visually shows the baby an attractive toy, while another person activates a noise from behind and to one side of the baby. The first person then observes whether the baby turned its head toward the sound.
The problem in these screening methods is that deaf children are visually alert, and can often out guess the testing procedure if there is the slightest visual clue as to where the sound is coming from. For example, a deaf child will see the extended arm moving, and will turn to see what is happening, or the deaf child will note that the second person has disappeared and will look around.
The present invention eliminates problems of this type by ensuring that the baby is aware of the testing individual on one side, and does not expect anything to happen on the other side. The testing individual then reaches around in back of the baby and sounds the audio stimulus of the invention on the back side of the baby, thereby misleading the baby as to where a sound could come from. In a study of the effectiveness of the invention about 60 presentations were made to deaf babies' ears, and only one head turn toward the sound occurred, this being a completely random head turn.
Attempts have been made to market electronic instruments that produce some variation of high frequency pure tone signals. These comprise generally two types: (1) high intensity warbled pure tone or narrow band instruments that identify severe deafness at birth or shortly thereafter, and (2) softer intensity pure tone instruments that are intended to identify milder hearing losses in children from birth to three years old.
For mild hearing loss in older children, as well as for severe hearing losses that might occur at or soon after birth, the most commonly used stimulus has been a "warble-tone", i.e. a pure tone that was "wobbulated" electronically. A 2000 Hz tone has been used in order to identify children who have a "nerve" hearing loss, this loss usually being more pronounced in the high frequencies than in the low frequencies.
The present invention operates upon the discovery that infants are much more attracted to the human voice than they are to the impersonal sound of a pure tone signal, however the signal is modified.
The problem of testing humans, including infants, for hearing loss has been addressed in the art.
The publication Hearing in Children, the second edition, copyright 1978, is of interest in that chapter 5 thereof contains a general discussion of "Clinical Audiologic Testing of Children". For example, at page 116 a table shows the "Auditory Behavior Index of Infants" and contains a "Noisemaker" and a "Startle to Speech" column. For example, at page 119 of this publication it is stated "toy noizemakers are the most useful signals" and at page 120 it is stated "Speech, pure tone, and noise audiometry through loudspeakers should be available--." Other testing parameters described in this publication include at page 118 the use of a 90 dB signal, at page 116 the use of a 40-60 dB signal, at page 117 isolation of the infant, at page 120 use of a 4,000 Hz signal at 25-35 dB at 3 inches distance, adt page 120 use of a 1,000 Hz signal 45- 55 dB at 3 inches distance, at page 120 use of a loud noise of 50-85 dB, and at page 116 speech at 65 dB.
U.S. Pat. No. 3,799,146 describes an arrangement wherein a series of test tones, of different levels of loudness, or a musical composition, are played through earphones as the subject is monitored for brainwave activity.
U.S. Pat. No. 3,938,500 describes a procedure whereby a subject's motor activity is monitored in response to unexpected audio stimulus. A cribside sound level of between 92 and 93 dB SPL is suggested, and at a frequency in the 2 to 4 kHz band.
U.S. Pat. No. 4,132,226 describes measuring the auditory threshold of marine mammals.
U.S. Pat. Nos. 4,489,610 and 4,759,070 describe computerized audiometers that generate a sequence of tones in real world hearing situation, and are capable of programming a hearing aid, and components thereof, for use by the person being tested.
U.S. Pat. No. 4,847,763 describes an audiometer wherein test signals of selectable kind and intensity may be used from a repertoire that is contained on a digital disk.
While prior devices, such as is exemplified above, are generally useful for their intended purposes, the art fails to provide a simple and inexpensive apparatus and method that is useful by unskilled and relatively untrained adults in providing reliable testing of infants for hearing defects.